Discovery 2. Manual — part 182

FRONT SUSPENSION

DESCRIPTION AND OPERATION

60-11

The ACE system uses a semi-synthetic hydraulic fluid which is the same as the fluid used for the PAS system. The
total capacity of the ACE system is 1.62 litres (0.42 US Gallons).

CAUTION: The ACE hydraulic system is extremely sensitive to the ingress of dirt or debris. The smallest
amount could render the system unserviceable. It is imperative that the following precautions are taken.

l

ACE components are thoroughly cleaned externally before work commences;

l

all opened pipe and module ports are capped immediately;

l

all fluid is stored in and administered through clean containers.

In the event of an ECU or hydraulic failure the system will fail safe to a 'locked bars' condition. The 'locked bars'
condition will allow the torsion bars to operate in a similar manner as conventional 'passive' anti-roll bars. Prolonged
cornering forces will allow a progressive increase in roll angle due to hydraulic leakage through the actuators and
valve block. Failures will be relayed to the driver by the illumination of the ACE warning lamp in the instrument pack.
Faults are recorded by the ECU and can be retrieved using TestBook.

When the ignition switch is moved to position II, the warning lamp will illuminate for two seconds to check functionality.
The warning lamp functionality can also be checked using TestBook.

TestBook must also be used to perform a bleeding procedure after maintenance operations have been performed to
ensure that complete system bleeding is performed. Trapped air in the system can seriously reduce the system
performance.

Fluid reservoir
The moulded plastic fluid reservoir is mounted on the left hand side of the engine compartment on a bracket which is
attached to the inner wing. The reservoir is dual purpose, being divided into two separate chambers; one for the ACE
system and one for the PAS system. Each chamber has its own filler neck and cap and is identified by moulded
lettering on the reservoir adjacent to each filler.

A non-serviceable filter assembly is fitted in the base of each chamber. The filter is made from fine stainless steel
mesh which is moulded into the body of the reservoir. The filter removes particulate matter from the fluid before it is
drawn into the hydraulic pump.

Upper and lower fluid level marks are moulded onto the reservoir body. The capacity of the ACE reservoir chamber
to the upper level mark is 0.5 litre (0.13 US Gallon).

FRONT SUSPENSION

60-12

DESCRIPTION AND OPERATION

Hydraulic pump

1 Outlet port
2 Cap
3 Piston spring
4 Piston
5 Inlet port
6 Cylinder housing
7 Shaft

8 Cam
9 Inlet housing

10 Spring
11 Discharge valve
12 Housing
13 Pulley attachment flange

The hydraulic pump is attached to a bracket on the left hand side of the engine and is driven at crankshaft speed by
the auxiliary drive belt. The pump is of the radial piston type which delivers fluid at high pressure.

The radial piston pump has six pistons located in bores in a cylinder housing. A central shaft, which is driven by a
pulley and the auxiliary drive belt, has a cam which operates the pistons as it rotates.

As the cam lobe reaches each piston, the piston is pushed outward, moving the fluid above the piston. The pressure
created by the fluid flow from the bore opens a spring loaded discharge valve and allows the fluid to flow to the pump
outlet port. When the piston reaches its full stroke, the flow reduces and the discharge valve closes under spring
pressure.

As the cam lobe moves away from the piston, a spring pushes the piston down the bore creating a vacuum above the
piston. As the piston moves down the bore, ports in the piston are exposed and connect with the fluid inlet. The
vacuum draws fluid into the piston filling the piston and the chamber above it. As the piston is again pushed upwards,
the ports are closed off by the bore and the fluid opens the discharge valve and flows to the outlet port.

FRONT SUSPENSION

DESCRIPTION AND OPERATION

60-13

The above sequence is applied to each of the six pistons for every revolution of the central shaft and cam. When the
engine is running the sequence occurs rapidly creating a constant flow of fluid. The fluid flow varies with the engine
speed and the rotational speed of the central shaft. The pressure felt at the actuator, created by the flow from the
pump, is controlled by the pressure control valve in the valve block.

The pump has a displacement of 8.5 cm

3

/rev and an operational pressure of 135 bar (1958 lbf.in

2

). The pump output

flow ranges from 7.0 l/min (1.85 US Gallons/min) at 775 rev/min to 9.25 l/min (2.44 US Gallons/min) at 7625 rev/min.

System pipes
Fluid is moved through the ACE system via a series of pipes and hoses. The pipes are mounted on brackets at
strategic points to assure quiet operation of the system.

The pipes from the pump to the valve block and from the valve block to the reservoir are one piece items which are
fitted at the factory before the body is attached to the chassis. If these pipes require replacement in service, the pipes
must be cut to facilitate their removal. 'In service' replacement pipes are available in two parts with a connector to seal
the joint.

The flexible hose which supplies pressure from the pump to the supply pipe attached to the front cross member is
fitted with an attenuator. The attenuator comprises a bullet shaped valve which is located between two spiral wound
springs held at each end of the flexible hose. This valve operates as a restrictor to damp pressure waves of hydraulic
fluid from the pump, reducing noise and strain on components downstream. The attenuator is integral with the supply
hose and pipe and cannot be serviced separately.

FRONT SUSPENSION

60-14

DESCRIPTION AND OPERATION

Valve block

1 Cap
2 'O' ring
3 Coil
4 'O' ring
5 Directional control valve 1 (extend)
6 Pressure transducer
7 Mounting bush 3 off
8 Valve block
9 'O' ring

10 High pressure filter
11 'O' ring
12 Cap

13 Stud 4 off
14 Pipe connections
15 Cap
16 'O' ring
17 Coil
18 'O' ring
19 Pressure control valve
20 Directional control valve 2 (retract)
21 'O' ring
22 Coil
23 'O' ring
24 Cap

The valve block directs hydraulic pressure to the actuators via solenoid operated directional control valves. A solenoid
operated pressure control valve regulates the required pressure to the actuators. The three valve solenoids are
controlled by signals received from the ACE ECU. A pressure transducer monitors the pressure delivered by the
pump. A replacable high pressure filter is installed into the lower face of the valve block and filters fluid before it
reaches the valves.

The valve block is located on the outside of the right hand chassis longitudinal. The valve block is secured to the
chassis with three bolts and rubber bushes. The rubber bushes isolate the valve block from the chassis, preventing
hydraulic noise from the valve block transmitting through the chassis and body.